How Metal Organic Chemical Vapor Phase Deposition (MOCVD) Works

The MOCVD technique enables very thin layers of atoms to be deposited on a semiconductor wafer and is a key process for manufacturing III-V compound semiconductors, especially gallium nitride (GaN)-based semiconductors.

Other names for the MOCVD process include: organo-metallic chemical vapor deposition (OMCVD), organo-metallic vapor phase epitaxy (OMVPE) and metal organic vapor phase epitaxy (MOVPE). The Close Coupled Showerhead® and the Planetary Reactor® technology are the two different technologies offered by AIXTRON for MOCVD deposition processes.

Close Coupled Showerhead® Technology

The Close Coupled Showerhead® technology (Figure 1) allows vertical introduction of chemicals into the process chamber, where the formation of semi conductor crystals occur. Similar to a showerhead, the gas introduction into the Close Coupled Showerhead® reactor is by means of several tiny gas channels in the reactor ceiling. This allows uniform distribution of the process gases along the whole surface of the wafer carrier. The showerhead is positioned very near the heated wafers.

Figure 1. Close Coupled Showerhead® 55x2 inch

Planetary Reactor® Technology

The horizontal laminar flow principle forms the basis of the Planetary Reactor® technology (Figure 2), where the process gas introduction into the deposition chamber is achieved using a special gas inlet (nozzle) at the center of the reactor ceiling. The gases are passed over the hot semiconductor substrates using a process pump by extracting them from the chamber edge and flowing them radially and uniformly from the chamber center to the edge, causing chemical breakup and subsequent reaction.

Figure 2. Planetary Reactor® 56x2 inch

By diffusing through the gas phase, the desired atoms deposit onto the surface of the wafer. A separate rotating disk, above which the wafer is placed, allows the materials to be deposited uniformly across the surface of the wafer. It is possible to modify the properties of the deposited layer by changing the introduced gases, enabling design and production of a superior quality semiconductor layer at an almost atomic scale.

AIXTRON MOCVD Production Platform

It is possible to integrate both the Planetary Reactor® and Close Coupled Showerhead® technologies into AIXTRON platforms, which have a highly modular and very flexible design known as an Integrated Concept (IC) system (Figure 3). The deposition process occurs within the platform system’s reactor chamber, allowing deposition of the semiconductor layers onto the substrate surface at different temperatures of up to roughly 1,200°C.

Figure 3. AIXTRON IC system

MOCVD for Compound Semiconductor Applications

III-V semi conductors or compound semiconductors are composed of elements of group III and V of the Periodic Table and are capable of interacting to produce crystalline compounds. They are advantageous in many ways over silicon semiconductors. The MOCVD process is used to fabricate the multilayer structures of these compound semiconductors, which are then processed into electronic or optoelectronic devices, including solar cells, high-speed transistors, laser diodes and LEDs.

The production of compound semiconductors involves vaporization and transportation of desired chemicals along with other gases into the reactor, where the chemicals are reacted to form the desired compound semiconductor. In the MOCVD process, a fine dose of ultra-pure gas is injected. AIXTRON MOCVD equipment provides cost-effective production solution to compound semiconductor manufacturers, thanks to its ability to deposit over larger surface areas.

Epitaxy represents the growth of thin, single layers deposited onto a suitable substrate into crystals. The MOCVD process allows uniform deposition of ultrathin film layers of below 1-nm-thick on substrates (Figure 4).

Figure 4. This diagram compares the diameter of an average human hair to the epitaxial layers on the substrate.

Laser diodes (Figure 5) must have atomic sharp layer interfaces and ultra high crystal quality for laser light generation. Transistors (Figure 6) are fabricated from a solid piece of semiconductor material and consist of at least three terminals to connect to an external circuit. III-V transistors are the critical electronic components of hybrid cars and mobile phones.

Figure 5. Laser diode

Figure 6. Transistors

Solar cells (Figure 7) transform solar energy into electricity using the photovoltaic effect. At present, silicon solar cells are predominantly available in the market. Solar cells made from compound semiconductors are principally used on satellites as they can withstand the radiation in space. They may now be utilized in concentrator solar cells for terrestrial applications.

Figure 7. Solar Cell

LEDs are compact light sources with low heat generation and low power consumption. These features make them a cost-effective and safe alternative to conventional lighting devices. Power LEDs are capable of delivering several hundred lumen output. After the MOCVD deposition process, the resulting wafers are then processed into LED chips. Based on the size of the chips, 4,000 to 120,000 LED chips can be fabricated from a four-inch wafer (Figure 8).

Figure 8. This diagram explains what LEDs are made of and how they work.

About Aixtron AG

AIXTRON AG is a leading provider of deposition equipment to the semiconductor industry. The Company's technology solutions are used by a diverse range of customers worldwide to build advanced components for electronic and opto-electronic applications based on compound, silicon, or organic semiconductor materials and more recently carbon nanostructures.

Such components are used in display technology, signal and lighting technology, fiber communication networks, wireless and cell telephony applications, optical and electronic data storage, computer technology as well as a wide range of other high-tech applications.

This information has been sourced, reviewed and adapted from materials provided by Aixtron AG.

For more information on this source, please visit Aixtron AG.

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